#include <stdio.h>

int main() {
    int n = 1, i, deno, nume;
    float sum = 0.0, this = 1.0;
    
    while (this > 0.0005) {
        sum += this;
        deno = 1;
        nume = 1;
        for (i = 1; i <= n; i++) {
            deno *= i;
            nume *= 2 * i + 1;
        }
        this = 1.0 * deno / nume;
        n++;
    }
    printf("pi/2: %f\n", sum);
    return 0;
}
